Electric circuit breaker



Aug. 29, 1961 L L, MANKQFF ErAL 2,998,499 ELECTRIC CIRCUIT BREAKER FildJune 4, 1958 2 Sheets-Sheet 1 Th ein@ Att CD1-vm e5.

Aug 29, 1961 l.. l.. MANKQFF ETAL 2,998,499

ELECTRIC CIRCUIT BREAKER 2 Sheets-Sheet 2 Filed June .4, 1958ATMOSPHEH/C PRESSURE TME 2,998,499 ELECTRIC CIRCUIT BREAKER .liawrenceL. Mankell, Drexel Hill, and August L. Str-eater, Broomall, Pa.,assiguors to General Electric Qontpany, a. corporation of New York FiledJune d, 1958, Ser. No.. 739,760 lo laims. (Cl. ZIEL-d50) This inventionrelates to an electric circuit breaker of the type in which acircuit-interrupting arc is established within a body of insulatingliquid and, more particularly, `relates to means for improving thedielectric strength of the insulating liquid immediately following acircuit-interrupting operation.

When a circuit-interrupting arc is established within a body ofinsulating liquid such as oil, the arc reacts with the oil to generate arapidly expanding gaseous bubble. The rapid expansion of this bubbleproduces an abrupt increase in the pressure of the surrounding liquid.This pressure increase continues until the arc has been extinguished, atwhich time the pressure of both the bubble and the liquid begins todrop. Tests have shown that, for high current interruptions, thispressure drop continues until the pressure of liquid and the bubble hasfallen to a very low value substantially below atmospheric pressure. Thepressure remains at approximately this negative value for several cyclesor more, after which it increases to a second peak, and thereaftercontinues to oscillate, though to a lesser extent.

During the time that the pressure is below atmospheric, the dielectricstrength of the insulating medium is at an undesirably low level.ri`here are a number of factors contributing to this low dielectricstrength. One factor is that the dielectric strength of a gas falls asits pressure drops. Another factor is that the reduced pressure allowsthe gas bubble to rapidly grow in physical size thereby decreasing thethickness of insulating liquid which is available to suppress breakdown.Still another actor is that the extreme low pressure causes gases thatare ordinarily dissolved in the liquid oil to be rapidly evolved, thusconverting a portion of the liquid into a sort of foam. This foam has asubstantially lower dielectric strength than clean oil. Thus, duringthis interval of negative pressure, the insulating medium, with itsdielectric strength impaired, is much less capable of suppressingincipient tlashovers, and accordingly, there is a much greater tendencyfor a destructive breakdown to occur through the insulating medium.

An object of the present invention is to provide for substantiallyincreased minimum pressures during the critical low pressure interval,thereby substantially increasing the dielectric strength of theinsulating medium during this interval.

Another object is to attain this result by means which does notobjectionably increase the peak positive pressures developed within thebreaker during any arcing condition to which it might be subjected.

In carrying out our invention in one form, we provide a circuit breakercomprising a tank of substantiaby ixed volume partially filled withinsulating liquid and the remainder with a gas disposed above theliquid. lieneath the liquid level there is provided circuit interruptingmeans which acts during a circuit interruption to generate within saidliquid a quantity of gases varying directly in accordance with thearcing energy developed during interruption. Also disposed beneath theliquid level is passage means aording communication bctween the gasabove the liquid and the region in which the arcing gases are generated,the passage means having in its region of minimum cross section apredetermined total effective area. Lining the internal walls of thetank is cusi'tioning means which has au eti surface ares Patent O 2 areacontacting the liquid at least several times as large as said totaleffective area of the passage means. The cushioning means has anavailable-compression volume in the range of 0.3 to 4 times the maximum-piantty of gases generated during the interruption of maximum ratedinterrupting current for the breaker. This volume of generated gases isassumed to be measured at atmospheric pressure, assuming an adiabaticexpansion to atmospheric pressure.

For a better understanding ot our invention, reference may be had to thefollowing description taken in connection with the accompanying drawing,wherein:

FIG. l is a iront elevational View partly in section of an oil circuitbreaker embodying our invention.

FIG. 2 is a sectional view taaken along the line 2 2 of FIG. l.

FIG. 3 is a graph illustrating the pressures developed within the tankof FIGS. l and 2 during the interruption of certain heavy currents.

FIG. 4 is a graph illustrating the manner in which cushions of varioussize affect certain minimum pressure relationships within the tank.

FIG. 5 is an enlarged sectional view taken along the line 5-5 of FIG. l.

Referring now to FIGS. l and 2, the circuit breaker shown thereincomprises a metallic tank lil comprising a body 1i of generalyellipsoidal form and a pair of spaced-apart cylindrical bushing pocketsl?. projecting divergently from the top of the tank body il. Supportedwithin the pockets l2 by means of annular end covers t3 suitably securedto the pockets are a pair of conventional high voltage terminal bushingsand At the inner ends of these bushings, circuit interrupters lo ot aconventional form are mounted. Each of these interrupters containssuitable separable contacts (not shown), which are electricallyinterconnected in series circuit relationship by means of a conductivecrossbar liti when the breaker is in its closed circuit position oi FIG.l. Since the details of the interrupters form no part of the presentinvention, they may assume any suitable conventional form, such as isdisclosed, for example, in US. Patent No. 12,749,412, McBride et al.,assigned to the assignee of the present invention. rlhe contacts withinthe interrupters are connected to power lines it? and 2@ at the top ofthe breaker by the usual conductive studs extending through the centersof the terminal bushings.

Control of the 1nulti-break circuit through the breaker is effected bylowering and raising the cross bar by means of a vertically-movableoperating rod 2li. F,This operating rod 2i is connected to a suitableoperating mechanism 2?. mounted within an enclosure 23 at the top of thetank itl. Actuation of the mechanism 2E; is effected by means of asuitable link extending into the enclosure through an opening scaled bysuitable means (not shown). The mechanism 22 is shown in simplified formas comprising a bcll-crank 2o pivoted at 27 and' having its armsrespectively coupled to the link 24 and the operating rod 2l. Themechanism enclosure 23 is spaced from the upper periphery of thc tankbody ll by means of a vertically extending pipe 25, which is shownclosely surrounding the operating rod 2li. The pipe 25 is suitablyjoined at its opposite ends to the enclosure 23 in the tank body il,respectively.

The bushing pockets l2 and the mechanism enclosure 23 are all vented tothe surrounding atmosphere at their upper ends by means of a suitablevent Sti located at the top of the enclosure 23. Conduits 33 and 3dinterconnect the interiors of the bushing pocket l2 and the enclosure 23so as to afford communication between the upper ends or the bushingpockets and the vent 59.

The tank l@ contains an arc-extinguishing insulating liquid. such asoil. At all tienes when the breaker is to un it,

a ed

operated, the oil lwithin the tank is maintained at a level which isdisposed above the uppermost periphery of the tank body ll and withinthe bushing pockets 12. The oil does not, however, completely fill thetank and, accordingly, a body of air normally at atmospheric pressure iscontained above the oil.

When the circuit breaker is tripped open from the closed position ofFIG. l, the cross bar l moves rapidly downward and causes each pair ofcontacts within the interrupters to separate and establish an arc. Eachof these arcs reacts with the surrounding oil to establish arapidly-expanding gaseous bubble. This rapid expansion of the bubbleproduces an abrupt increase in the pressure of the surrounding liquid,and this increase continues until the are has been extinguished. Whenthis occurs, the pressure of both the bubble and the liquid begins todrop, and this drop continues until the pressure reaches a minimum valuewhere it generally remains for several cycles or more. A typical mannerin which the pressure of the liquid first rises and then falls isillustrated in u FIG. 3, in which curve A is a graph illustrating thepressure of the liquid within the tank during and following a typicalhigh current circuit interruption. The values of pressure depicted arerepresentative of those encountered with a tank such as 10, but withoutthe cushioning means of our invention. For such a tank without thecushioning means, the pressure of the gas bubble corresponds to and issubstantially equal to that of the liquid. Accordingly, curve A alsodepicts the bubble pressure for a tank such as 10 Without the cushioningmeans. As will be apparent from FIG. 3, the low pressure interval isfollowed by another rise in pressure, this time to a second peak whichis lower than the iirst peak. The pressure then falls and continues tooscillare, though to a progressively lesser extent.

Both the maximum pressure reached and the minimum pressure reached aredependent upon the amount of arcing gases generated, which, in turn, isdependent upon the amount of energy liberated by the arc before itsextinction. For low current interruptions, where the arcing energy isrelatively low, the volume of gases generated is correspondingly low andas a result the maximum pressures. reached are relatively low and theminimum pressures reached are relatively high. For high currentinterruptions, however, much larger quantities of gases are generated,and this causes the positive peak pressures to be much higher and theminimum pressures to be much lower. For example, for extreme highcurrent interruptions, tests have shown that, for conventional tanks(e.g., the tank 10 without the cushioning means of our invention), thepressure of the oil during the rst negative swing can fall to values aslow as about l1 or 12 p.s.i. below atmospheric.

Extreme low pressures, such as those developed as a result of highcurrent interruptions, can very seriously reduce the dielectric strengthof the insulating medium during the low pressure interval. This can leadto destructive ilashovers through the insulating medium, for example,from the high voltage interrupter to the grounded tank, during this lowpressure interval.

There are several factors which are believed to be responsible for thelow dielectric strength during the low pressure interval. One is thatthe dielectric strength of the gas decreases as its pressure decreases,with the result being that the dielectric strength of the gas within thebubble decreases as its pressure falls. Another factor is that thereduced liquid pressure allows the bubble to rapidly grow in sizethereby decreasing the thickness y of the insulating liquid which isavailable to suppress breakdown, e.g., the liquid between the bubble andthe tank wall. Still another factor is that the extreme low pressurecauses gases that are ordinarily dissolved in the liquid oil to berapidly evolved, thus converting a portion of the liquid into a sort offoam having a substantially lower dielectric strength than clean oil.

Studies made of the above-described pressure oscillations indicate thatthe negative pressure swing results from the kinetic energy of the oildisplaced into the air chamber at the top of the tank by the gaseousarcgenerated bubbles. The oil, in moving away from the rapidly-expandingbubbles, attains substantial kinetic energy, especially during highcurrent interruptions. The body of air at the top of the tank tends tooppose this upward movement of the oil mass, but since the body of airis relatively large and is vented to atmosphere, it can exert only minoropposition to the moving oil mass. As a result, the oil mass keepsmoving, even after the arc is extinguished, thus allowing the gasbubbles to continue expanding. This continued expansion when no arcinggases are being generated lowers the pressure of both the bubbles andthe surrounding liquid to the objectionably low values describedhereinabove. Finally the bubble pressure becomes low enough to enablethe atmospheric pressure at the top of the tank to stop the oil mass andto start it moving back toward the low pressure bubbles. Once the massof oil becomes accelerated in reverse toward the gas bubble itovershoots equilibrium pressure, giving rise to the second pressure peakpreviously mentioned.

Constructing the circuit breaker in accordance with the presentinvention has resulted in very materially increasing the minimumpressures developed during the above described low pressure interval. Incarrying out our invention in one form, we have lined a lar-ge area ofthe internal wall of the tank with a layer of resilient cushioningmaterial. This layer of cushioning material is preferably in the form ofa closed-cell sponge 40 made of a synthetic rubber which is highlyresistant to oil deterioration, such as, for example, the syntheticrubber sold under the trademark Buma-N. The closed cells of the sponge40 are gas filled, preferably with nitrogen. Sponge material of thischaracter is commercially available under the trademark Rubatex and isfurther characterized by its lack of absorbency Awith respect to liquidsin which it is immersed.

This sponge material 40 can be attached to the tank walls in anysuitable manner, but, as shown in FIGS. 2 and 5, we prefer to rely uponsuitable studs 42 fixed to the tank wall and projecting through thesponge 40. Suitable strips 44 having'holes therein registering with thestuds 42 are disposed on the inner side of the sponge 40. These stripsare clamped against the sponge by nuts i6 threaded on the studs, andthus act to secure the sponge in place against the tank wall. When theinterrupter is operated to establish circuitinterrupting arcs within theoil, the rapidly expanding gaseous bubble forces the surrounding oilprimarily toward the resilient cushion 40 instead of up into the airpocket at the top of the tank. This compresses the gas within thecushion and thus causes the cushion to develop a relatively largeopposing force before the pressure in the bubble can swing belowatmospheric pressure. This opposing force counterbalances the forces dueto the kinetic energy of the oil mass and thus very substantially raisesthe aforo-mentioned minimum pressures resulting from this kineticenergy.

The ability of the cushion to act effectively to limit the negativepressure swings depends upon a number of important factors. For example,it is important that the internal surface area of the cushion in contactwith the oil be at least several times greater than the access area tothe body of air at the top of the tank. This access area is the totalarea of all passages leading from the region where the gas bubbles areinitiated to the air chamber at the top of the tank, measured in theregion where the passages have their minimum cross section. For example,inthe disclosed tank this access area would be the total internal crosssectional of the two bushing pockets 12 and the pipe 25, minus the crosssectional area of the bushings t4 and 15 and the operating rod 2li,measured approximately along the line A-A.

ln general, the greater' the ratio of the cushion area to the accessarea, the greater will be the influence of the cushion in controllingthe pressure peaks and the weaker will be the influence of the airchamber. This is due to the fact that increasing this ratio causes arelatively greater proportion of the oil displaced by the arcing bubblesto be moved toward the cushion rather than toward the air chamber. Byhaving the surface area of the cushion at least several times largerthan the access area, most of the oil so displaced moves toward thecushion rather than toward the air chamber, thus allowing the cushion toexert a predominating efiect on. the pressure peaks.

lt is also important that the cushioning material have a rather limitedavailable-compression volume. This term, as used in this application,may be defined as that volume of the cushion which is available forcompression by the arc-generated pressures. For example, with agas-filled sponge, the available compression volurne is the volumeoccupied by the gas in the sponge, referred to standard atmosphericpressure and temperature (i.c., about C.). This available compressionvolume for a cushion relying upon a gas the compressible medium shouldfall within a range of about 0.3 to 4 times the largest volume of gasgenerated by the breaker at full interruptingy rating (assuming thegencrateri-gas volume to be measured at atmospheric pressure after anadiabatic expansion to atmospheric pressure). ribis is illustrated inthe graph of FIG. 4 `which depicts on its ordinate the approximateminimum prcssures that will be developed with cushions of differingavailablocompression volumes. The available compression volume isplotted on a logarithmic scale on the abscissa of the graph in terms ofthe ratio of the available compression volume to the maximum volume ofgases that will be generated (referred adiabatically to atmosphericpressure). The curve is based upon tests and calculations with a tanksuch as depicted at lill in the drawings, where the effective cushionarea is at least several times the access arca to the air pocket at thetop of the tank lll and, more particularly, in the neighborhood of tentimes the access area.

Referring to the curve, the minimum pressure that will be developed whenno cushion is present is indient ed at the point where the curve crossesthe ordinate ol." the graph, ie., at abo-ut 3 psi. absolute. Assume nextthat cushions of predetermined available-compression volumes areutilized. With a cushion having an avail` able compression volume ofabout 0.3 times the maxiA mum volume of generated gas, the bubblepressure roughly doubled, and this produces a substantial increase inthe dielectric strength of the insulating medium etween the interruptorand the tank. The maximum increase in bubble pressure and, hence, indielectric strength occurs when the available compression volume isbetween one and two times 'the maximum volume of gases generated. lnthis preferred range, the minimum pressure has been more than tripledand the dielectric strength of the overall insulating medium has beenincreased by about 50% as compared to that obtained without a cushion.

Increasing the cushion volume beyond this preferred range reduces theminimum bubble pressure, and if the plotted volume ratio exceeds a valueof about four, thc minimum pressure falls to appreciably less than twicethat obtained without the cushion. Such relatively low minimum pressuresproduce correspondingly low values of dielectric strength, with theresult being that the cushion is operating relatively inelliciently whenof such a large volume. As an example, of such incllicieney. when thecushion volume is ten times the overall bubble volume, the minimumpressure is only about one psi n without.. the. cushion, .il its o Llila very slight increase in the dielectric strength of the overallinsulating medium. The probable explanation for the poor resultsobtained with cushions of such rela* tively large volumes is that suchcushions are capable o= developing no appreciable opposing force to theoutwardly moving oil mass before the pressure in the gas bubble swingsto an objectionably low value.

To illustrate the manner in which the cushion 4@ affects the gas bubblepressure, a curve B has been included in FlG. 3. This curve, which isbased upon tests and calculations, depicts the approximate gas bubblepressures developed with a cushion having (l) an available compressionvolume substantially equal to the largest volume of gas generated by thebreaker at full interrupting rating (assuming that the generated gasvolume is referred adiabatically to atmospheric presu sure) and (2) aneffective area of approximately l@ times the access arca leading to theair pocket at the top of tank Elli. As will be apparent from curve thegas pressure, in falling from its peak, drops to a minimum value ofabout 9 p.s.i. absolute, as compared to the 3 psi. absolute minimumvalue resulting from operation without the cushion, as is illustrated bycurve A. This higher minimum pressure of curve B results in asubstantially higher dielectric strength of the in sulating medium inthe tank during the critical interval after interruption and, hence, inmuch less likelihood of a breakdown to the tank.

ln the above description, no mention has been made of the resilience ofthe walls of the the tank itself. These walls yield slightly in responseto the maximum pressure peaks, but in a tank of the construction shownin the drawings, this increased volume is so slight as to be practicallynegligible. However, for a tank which might have walls of a moreyieldable nature, expansion ot' the tanl; itself becomes a :moresignificant factor. To compensate for such tank expansion, the cushionvolume should be reduced by an amount equal to the increase in tantivolume resulting from tank expansion in response to an internal pressureof about psi. gage. For a tank of the construction shown in thedruif/ing, tank expansion in response to such a pressure is practicallynegligible and, thus, the lower limit for the cushion volume, ie., about0.3 times the maximum 'volume of generated remains substantiallyunchanged.

Since the cushion area must be large in comparison to thepreviously-described arca leading to the air chamber at the top olf thetank, it is desirable that this access area be relatively small in.order to hold the cushion area within practical limits. 'Libere is,however, a certain minimum value, above which this access aren should bemaintained. in this regard, it eornetimes hap pens that an arc developsbetween the it'ilerrupter and the tank, say as a result of a lightningstriking the breaker or connected power line. Opening of the breakeritself@ might have no eliect on such au nrc, and to terminato such annrc, it is usually necessary that one or more back up circuit breakersbe opened. rlhis usually requires least live or more cycles, Le., l/lgof a second or more, and during this relatively prolonged interval thetank must be capable of safely accomnioduting the gases that would begenerated by such arcing. To meet this ren quirement, the access arealeading to the air pocket should be large enough to allow the liquiddisplaced by arcing gases under such circumstances to flow into the airpocket at a rate sufficiently high to prevent damaging pressures fromdeveloping within the tank. The volume of thc air pocket and the size oiits vent also must large enough to rallow the tank to safely accommodatethe liquid displaced under such circumstances. In the disclosed tank,for example, we prefer that the air pocket be about 30 times the maximumvolume of gases that would be generated by the breaker at its fullinterrupting rating (referring this volume adiabatically to atmos phericpressure). The 4rent ,meier-ably should be at ica "27 several inches indiameter, it being understood that enlarging the vent allows certainreuctions to be made in the volume of the air pocket. Thus, the accessarea and the air pocket should be large enough to hold to a safe levelthe maximum pressure that will be developed within the tank during z ofa second of arcing to tank. A value of S0 p.s.i. gage is a practicalupper -limit for the maximum pressure permissible under this lattercondition.

Constructing the cushioning means from a closed-cell sponge isespecially advantageous for a number of reasons. First of all, the gasentrapped within the sponge is completely isolated from the oil andtherefore is not subject to being absorbed Iby the oil, as is the casein cushions where gas-to-oil contact is present. In addition, the spongeis much more resistant to mechanical damage than most other types ofcushions, e.g., bladders and the like, inasmuch as a puncture results inonly an insignificant loss of entrapped gas from the sponge. Thespongetype of cushion is also advantageous in being readily adaptable totanks of varying sizes and shapes and in providing a relatively largesurface area per unit of volunie.

While a circuit breaker tank of the general configuran tion shown in thedrawing is especially well suited to the practice of the presentinvention, it is to be understood that the invention is also applicable,at least in its broader aspects, to tanks of other configuration.

It will be apparent to those skilled in the art that various othermodifications may be made without departing from the invention in itslbroader aspects, and we, therefore, intend in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electric circuit breaker comprising a metallic tank, a body ofinsulating liquid partially lilling said tank and a body of gas normallyat approximately atmospheric pressure within said tank disposed abovesaid liquid, circuit-interrupting means acting during a circuitinterruption to generate within said liquid a quantity of gases varyingdirectly in accordance with the arcing energy developed duringinterruption, passage means disposed beneath the level of said liquidand affording communication between the gas disposed above said liquidand the region in which said arcing gases are generated, said passagemeans having in its region of minimum cross-section a predeterminedtotal elective area, cushioning means lining the internal walls of saidtank and having an eleetive surface area contacting said liquid at leastseveral times as large yas said total effective area of saidfpassagemeans, the maximum quantity of gases generated by said interruptingmeans during interruption of any currents within the interrupting ratingof the breaker having a predetermined volume measured at atmosphericpressure assuming an adiabatic expansion to atmospheric pressure, saidcushioning means having an available-compression volume generally in therange of one to two times said predetermined volume minus the increasedavailable volume resulting from tank expansion in response to aninternal pressure of about 45 p.s.i. gage.

2. An electric circuit breaker comprising a metallic tank, a body ofinsulating liquid partially filling said tank and a body of gas normallyat approximately atmospheric pressure within said tank disposed abovesaid liquid, circuit-interrupting means acting during a circuitinterruption to generate within said liquid a quantity of gases varyingdirectly in accordance with the arcing energy developed duringinterruption, passage means disposed beneath the level of said liquidand affording communication between the gas disposed above said liquidand the region in which said arcing gases are generated, said passagemeans having in its region oi minimum crosssection a predetermined totaleffective area, cushioning means lining the internal walls of said tankand having au eiiective surface area contacting said liquid at leastseveral times as large as said total eiective area oi said passagemeans, the maximum quantity of gases generated by said interduptingmeans during interruption of any currents within the interrupting ratingof the breaker having a predetermined volume measured at atmosphericpressure, assuming an adiabatic expansion to atmospheric pressure, saidcushioning means having an availablecompression volume in the range ofabout 0.3 to 4 times said predetermined volume minus the increasedavailable volume resulting from tank expansion in response to aninternal pressure of about 45 p.s.i. gage.

3. The circuit breaker of claim l in which said access area issuliciently large and said body of gas is of sutli` ciently large volumeto allow an arc of maximum rated current to be maintained t0 the tankfor a period of at least 1%2 second without developing pressuresulicient to damage the circuit breaker.

4. The circuit breaker of claim 2 in which said access area issuiiiciently large and said body of gas is of suiiiciently large volumeto allow an arc of maximum rated current to be maintained to the tankfor a periodvof at least g second without developing pressure sufficientto damage the circuit breaker.

5, An electric circuit breaker comprising a metallic tank, a body ofinsulating liquid partially filling said tank and a body of gas normallyat approximately atmospheric pressure within said tank disposed abovesaid liquid, circuit-interrupting means acting during a circuitinterruption to generate within said liquid a quantity of gases varyingdirectly in accordance with the arcing energy developed duringinterruption, passage means disposed beneath the level of said liquidand affording communication between the gas disposed above said liquidand the region in which said arcing gases are generated, said passagemeans having in its region of minimum cross-section a predeterminedtotal effective area, cushioning means lining the internal walls of saidtank and having an elective surface area contacting said liquid at leastseveral times as large as said total effective area of said passagemeans, the maximum quantity of gases generated by said interruptingmeans during interruption of any currents within the interrupting ratingof the breaker having a predetermined volume measured at atmosphericpressure assuming an adiabatic expansion to atmospheric pressure, saidcushioning means having an available-compression volume generally in therange of one to two times said predetermined volume minus the increasedavailable volume resulting from tank expansion in response to aninternal pressure of about 45 p.s.i gage, said cushioning meanscomprising sponge material lining the internal walls of said tank, saidsponge material being of a closedcell, gas-filled cell construction.

6. An electric circuit breaker comprising a metallic tank, a body ofinsulating liquid partially filling said tank and a body of gas normallyat approximately atmospheric pressure within said tank disposed abovesaid liquid, circuitdnterrupting means acting during a circuitinterruption to generate within said liquid a quantity of gases varyingdirectly in accordance with the arcing energy developed duringinterruption, passage rneausv disposed beneath the level of said liquidand affording communication between the gas disposed above said liquidand the region in which said arcingV gases are generated, said passagemeans having in its region of minimum cross-section a predeterminedtotal effective area, cushioning means lining the internal walls of saidtank and having an effective surface area contacting said liquid atleast several times as large as said total effective area of saidpassage means, the maximum quantity of gases generated by saidinterrupting means during interruption of any currents within theinterrupting rating of the breaker having a predetermined volumemeasured at at= mospherie pressure, assuming an adiabatic expansion toatmospheric pressure, said cushioning means having auavailable-compression volume in the range ot about 0.3

to 4 times said predetermined volume minus the increased availablevolume resulting from tank expansion in response to an internal pressureof about 45 p.s.i. gage, said cushioning means comprising spongematerial lining the internal walls of said tank, said sponge materialbeing of a closed-cell, gas-filled cell construction.

7. ln an electric circuit breaker, a metallic tank cornprising a bodyportion of generally ellipsoidal configuration and a pair of tubularbushing pockets projecting outwardly from the upper part of the saidbody portieri, a body of insulating liquid filling said tank to aminimum level disposed within said bushing pockets and a body of gasnormally at aproximately atmospheric pressure disposed within said tankabove said liquid, terminal bushings extending through said pockets intosaid tank body, circuit-interrupting means located Iat the inner end ofsaid terminal bushings and acting during a circuit interruption togenerate within said liquid a quantity of gases varying directly inaccordance with the arcing energy developed during interruption, passagemeans dis posed beneath the level of said `liquid and alordingcommunication between the gas disposed above said liquid and the regionin which said arcing -gases are generated, said passage means having inits region of minimum crosssection a predetermined total etective area,cushioning moans lining the internal walls of said tank and having aneiective surface area contacting said liquid at least several times aslarge as said total etiecti've area of said passage means, the maximumquantity of gases generated by said interrupting means duringinterruption of any currents within the interrupting rating of thebreaker having a predetermined volume measured at atmospheric pressureassuming an adiabatic expansion to atmospheric pressure, said cushioningmeans having an available-com-l pression volume generally in the rangeof one of two times said predetermined volume minus the increasedavailable volume resulting `from tank expansion in response to aninternal pressure of about 45 fp si. gage.

8. in an electric circuit breaker, a metallic tank cornprising la bodyportion of generally ellipsoidal configura tion and a pair of tubularbushing pockets projecting o-utvvardly from the upper part of the saidbody portion, a body of insulating liquid filling said tank toa minimumlevel disposed within said bushing pockets and a body of gas normally atapproximately atmospheric pressure disposed within said tank above saidliquid, terminal bushings extending through said pockets into said tankbody, circuit-interrupting means located at the inner end of saidterminal bushings and acting during a circuit interruption to generatewithin said liquid a quantity of gases varying directly in accordancewithy the arcing ener-I gy developed during interruption, passage meansdisposed beneath the level of said liquid and yaffording communicationbetween the gas disposed above said liquid and the :region iu which saidarcing gases are generated, said passage means having in its region ofminimum cross-section a predetermined total effective area, cushioningmeans lining .the internal ywalls of said tank and having an eicc tivesurface area contacting said liquid at least several times as large assaid total effective area of said passage means, the maximum quantity ofgases generated by said interrupting means during interruption of anycurrents within the interrupting rating of the breaker having apredetermined volume measured at atmospheric pressure assuming anladiabatic expansion to atmospheric pressure, said cushioning meanshaving an available-compression volume generally in the range of 0.3 to4 times said predetermined volumc minus increased available volumercsulting from tank expansion in response to an internal pressure ofabout 45 p.s.i. gage.

y9. in an electric circuit breaker, a metallic tank, a pair of terminalbushings projecting into said tank at the upper end of said tank, saidtank comprising a lower portion generally semi-ellipsoidal in shape andan dner porn tcrial lining the ing liquid `filling said tank to a levelabove the inner ends of said bushings and a body of gas normally atapproximately atmospheric pressure disposed within said tank above saidliquid, circuit interrupting means at the inner ends of said bushingsacting during a circuit-interrupting operation to generate within saidliquid a quantity of gases varying directly in accordance with thearcing energy developed during interruption, means extending into thevicinity of said bushings and defining beneath the level of said liquidrestricted passage means affording cornmunication between the gasdisposed above said liquid and the region in which said arcing gases aregenerated, said passage means having in its region of minimumcrosssection a predetermined total effective area, cushioning meanslining the internal walls of said tank and having an effective surfacearea contacting said liquid at least several times as large as saidtotal eiiective area of said passage means, the maximum quantity ofgases generated by said interrupting means during interruption of anycurrents within the interrupting rating of the breaker having apredetermined volume measured at atmospheric pressure assuming anadiabatic expansion to atmospheric pressure, said cushioning meanshaving an available-compression volume generally in the range of one totwo times said predetermined volume minus the increased available volumeresulting from tank expansion in response to an internal pressure ofabout 45 p.s.i. gage.

l0. In an electric circuit breaker, a metallic tank, a pair of terminalbushings projecting into said tank at the upper end of said tank, saidtank comprising a lower portion generally semi-ellipsoidal in shape andan upper por tion supporting said terminal bushings, a body ofinsulating liquid tilting said tank to a level above the inner ends ofsaid bushings and a body of gas normally at approximately atmosphericpressure disposed within said tank above said liquid, circuitinterrupting means at the inner ends of said bushings acting during acircuit-interrupting operation to generate within said liquid a quantityof gases varying directly in accordance with thc arcing erh ergydeveloped during interruption, means extending into the vicinity of saidbushings and defining beneath the level of said liquid restrictedpassage means aiording communication between the gas disposed above saidliquid `and the region in which said arcing gases are genu erated, saidpassage means having in its region of mir1imum cross-section apredetermined total cii'cctive arca, cushioning means lining thcinternal walls of said tank and having an effective surface arcacontacting said liquid at least several times as large as said totaleffective area of said passage means, the maximum quantity of gasesgenerated by said interrupting means during interruption of any currentswithin the interrupting rating of the breaker having a predeterminativolume measured at atmospheric pressure assuming an adiabatic expansionto atmospheric pressure, said cushioning means having anavailabio-corttpiession volume generally in the range of 0.3 to 4 timessaid predetermined volume minus the increased available volume resultingfrom tank expansion in response to an internal pressure of about 45 psi.gage.

lil. An electric circuit breaker comprising a metallic tank ofsubstantially constant volume, a body of insulab ing liquid partiallyfilling said tank and a body of gas normally at approximatelyatmospheric pressure within'v said tank disposed above said liquid,circuit-interrupting means acting during a circuit interruption togenerate within said liquid a quantity of gases varying directly inaccordance with the arcing energy developed during interruption, passagemeans disposed beneath the level of said liquid `and affordingcomn'iunication between the gas disposed above said liquid and theregion in which said arcing gases are generated, said passage meanshaving in its region of minimum cross-section a predetermined totaletective area, cushioning means formed of sponge mainternal walls ofsaid tank and having :ze sting iiquid. at im bi te;

several times as large as said total effective `area of said passagemeans, the maximum quantity of gases generated by said interruptingmeans during interruption of any. 'currents within the interruptingrating of the breaker having a predetermined volume measured atatmospheric pressure assuming an adiabatic expansion to atmosphericpressure, said sponge material comprising closed-cells `filled withigas,thc `total volume of gasin said cells measured at standard atmosphericpressure and temperature being in the range of about 0.3 to 4 timessaidprcclctermincd volume.

l2. The circuit breaker of claim 11 in which the ltotal volume of gas insaid closed cells, measured at standard atmospheric pressure andtemperature, is in the range of one to two times said predeterminedvolume.

13. An electric circuit breaker comprising a tank containing insulatingliquid, an interrupter disposed within 14. The circuit ybreaker oflclaim 1 in which said cushioning means has an effective surface areacontacting said liquid at least in the neighborhood of ten times aslarge as said total effective area of said passage means.

15. The circuit breaker of claim 2in which said cushioning means has aneffective surface area contacting said liquid at least in theneighborhood of ten times as large as said total effective area of saidpassage means.

16. The circuit breaker of claim 6 in which said cushioning means has aneffective surface area contacting said liquid at least in theneighborhood of ten times as large as said total effective area of saidpassage means.

Reterenccs Cited in the tile of this patent UNITED STATES PATENTS1,566,091 Hilliard Dec. 15, 1925 1,631,681 Hilliard June 7, 19271,699,144 Hilliard Jan. 15, 1929 2,061,945 Koppelmann et al Nov. 24,1936 2,080,612 Kesselring et al May 18, 1937 2,734,973 MacNeill et al.Feb. 14, 1956 2,835,769 Milne et al. May 20, 1958 FOREIGN PATENTS131,953 Austria Feb. 25, 1933 518,314 Great Britain Feb. 23, 1940942,976 France Sept. 27, 1948

